The use of a stent to establish and maintain patency in an otherwise occluded vessel in the cardiovascular system of a patient has been a preferred surgical procedure for many years. By way of a general overview of such a procedure, the stent is delivered through the affected vessel to the site of the lesion causing the occlusion. At the lesion site, the stent is implanted to obviate the effects of the lesion. To do this, a balloon catheter is typically used as a delivery system. An example of such a stent, and a method for its use, is provided by U.S. Pat. No. 5,133,732 which issued to Wiktor for an invention entitled "Intravascular Stent," and which is assigned to the same assignee as the present invention.
In order to use a balloon catheter for a stent delivery system, the stent is positioned around the balloon with the stent in a compressed configuration. In its compressed configuration, the stent is designed to present the small profile that is necessary for advancement of the stent through the vessel of the patient. Once at the site of the lesion, the balloon is inflated to reconfigure the stent from its compressed configuration into an expanded configuration. This reconfiguration expands the stent against the lesion. The balloon is then deflated to disengage the balloon from the stent which has now been permanently reconfigured into its expanded configuration. Lastly, the balloon catheter is removed from the patient, while leaving the expanded stent in place at the site of the lesion.
When a balloon catheter is used as part of a stent delivery system, it is, of course, desirable for the stent to remain in position on the balloon catheter until such time as the balloon is inflated by the physician. It is, however, also desirable for the stent to be easily disengaged or detached from the balloon after the balloon has been inflated by the physician. As a practical matter, it is necessary to keep the stent from slipping off the balloon before the stent has been delivered to the site of the lesion.
It happens that the stent, and the balloon on which it is carried, are both elongated structures which generally define respective longitudinal axes. Accordingly, when the stent and balloon are joined together they are effectively coaxial. In this configuration, separation of the stent from the balloon is most likely to occur by movement of the stent over the balloon in an axial direction relative to the balloon. Consequently, a resistive retention force, which is axially aligned with the stent and balloon, and which acts between the stent and the balloon, will help prevent premature separation of the stent from the balloon.
Heretofore, in order to retain a stent on a balloon, many stent delivery systems have relied only on the forces which result when the stent is crimped onto the balloon. Consequently, the desired results of this crimping action has been two-fold. For one, this crimping is intended to compress the stent into a low profile configuration. For another, the crimping was intended to generate accompanying forces between the balloon and the stent which will hold the stent on the balloon. The crimping forces, however, are generally applied in a radial direction relative to the balloon and stent and, as such, do not specifically establish axially oriented retention forces. Thus, with only crimping, there are no designed axial forces which will prevent or inhibit axial movement of the stent over the balloon. The situation is only aggravated when a slippery, low friction, material is used for the manufacture of the balloon.
There are, of course, methods other than crimping which have been suggested for holding a stent on a balloon. For example, in U.S. Pat. No. 4,733,665, the catheter includes retaining ring members at the proximal and distal ends of the stent to assist in retaining it on the balloon. Also, U.S. Pat. No. 5,632,760 discloses bulges which are locked proximal and distal to the stent to hold the stent on the balloon. As another example, U.S. Pat. No. 5,643,278 discloses a sheath which is deployed over the stent to retain it during delivery. Additionally, this patent discloses use of a frangible glue to hold the stent on the balloon.
In light of the above, it is an object of the present invention to provide a stent delivery catheter system, and a method for manufacturing a stent delivery catheter, which enhances the interactive forces between the stent and the balloon that prevent or inhibit axial movement of the stent over the balloon before the balloon is inflated. Another object of the present invention is to provide a stent delivery catheter system, and a method for manufacturing a stent delivery catheter, which allows for easy disengagement of the balloon from the stent when the balloon subsequently deflated after having been inflated to expand and position the stent at the site of a lesion in a patient's vessel. Still another object of the present invention is to provide a stent delivery catheter system (and a method for manufacturing a stent delivery catheter) which is easy to use, simple to manufacture and comparatively cost effective.